U.S. patent application number 12/910046 was filed with the patent office on 2011-05-05 for optical device.
This patent application is currently assigned to TOHOKU UNIVERSITY. Invention is credited to Rintaro Koda, Masaru Kuramoto, Takao Miyajima, Tomoyuki Oki, Hideki Watanabe, Hiroyuki Yokoyama.
Application Number | 20110103419 12/910046 |
Document ID | / |
Family ID | 43925393 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110103419 |
Kind Code |
A1 |
Koda; Rintaro ; et
al. |
May 5, 2011 |
OPTICAL DEVICE
Abstract
The present invention provides an optical device capable of
suppressing a drive current and an optical output to be varied with
a passage of the time. The optical device includes: an optical
element including a first end face and a second end face, and
emitting light having a wavelength from 300 nm to 600 nm both
inclusive at least from the second end face in the first end face
and the second end face; a pedestal including a supporting
substrate supporting the optical element, and a connecting terminal
electrically connected to the optical element; and a sealing
section including a light transmitting window in each of a portion
facing the first end face and a portion facing the second end face,
and sealing the optical element.
Inventors: |
Koda; Rintaro; (Tokyo,
JP) ; Miyajima; Takao; (Kanagawa, JP) ;
Watanabe; Hideki; (Kanagawa, JP) ; Yokoyama;
Hiroyuki; (Miyagi, JP) ; Oki; Tomoyuki;
(Kanagawa, JP) ; Kuramoto; Masaru; (Kanagawa,
JP) |
Assignee: |
TOHOKU UNIVERSITY
Miyagi
JP
Sony Corporation
Tokyo
JP
|
Family ID: |
43925393 |
Appl. No.: |
12/910046 |
Filed: |
October 22, 2010 |
Current U.S.
Class: |
372/45.01 ;
359/333; 359/344; 359/346 |
Current CPC
Class: |
H01S 5/1085 20130101;
H01S 5/005 20130101; B82Y 20/00 20130101; H01S 5/02253 20210101;
H01S 5/02212 20130101; H01S 5/34333 20130101; H01S 5/0655 20130101;
H01S 5/0021 20130101; H01S 5/028 20130101; H01S 5/2009 20130101;
H01S 5/2201 20130101; H01S 5/14 20130101; H01S 5/1014 20130101;
H01S 5/2214 20130101; H01S 5/4006 20130101; H01S 5/50 20130101 |
Class at
Publication: |
372/45.01 ;
359/333; 359/344; 359/346 |
International
Class: |
H01S 5/00 20060101
H01S005/00; H01S 3/02 20060101 H01S003/02; H01S 3/08 20060101
H01S003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2009 |
JP |
2009-250624 |
Mar 2, 2010 |
JP |
2010-045394 |
Claims
1. An optical device comprising: an optical element including a
first end face and a second end face, and emitting light having a
wavelength from 300 nm to 600 nm both inclusive at least from the
second end face in the first end face and the second end face; a
pedestal including a supporting substrate supporting the optical
element, and a connecting terminal electrically connected to the
optical element; and a sealing section including a light
transmitting window in each of a portion facing the first end face
and a portion facing the second end face, and sealing the optical
element.
2. The optical device according to claim 1, wherein each light
transmitting window contains a transparent member in which an
antireflection film is formed on a surface.
3. The optical device according to claim 1, wherein the optical
element serves as an optical amplifying element amplifying the
light incident into the first end face, and emitting the light
having a luminance larger than that of the incident light at least
from the second end face in the first end face and the second end
face.
4. The optical device according to claim 3, wherein each of the
first end face and the second end face has an antireflection film
on the surface.
5. The optical device according to claim 3, wherein the optical
element is directed toward the first end face in a direction that
the first end face and the light transmitting window do not
frontally face each other.
6. The optical device according to claim 3, wherein the optical
element contains a wurtzite semiconductor crystal.
7. The optical device according to claim 3, wherein the optical
element contains AlGaInN.
8. The optical device according to claim 3, further comprising: a
first lens between the light transmitting window and the first end
face; and a second lens between the light transmitting window and
the second end face.
9. The optical device according to claim 3, wherein the transparent
member has a lens function.
10. The optical device according to claim 3, wherein when the light
having the wavelength from 300 nm to 600 nm both inclusive is
incident into the first end face, and stimulated emission is
generated by the incident light, each of the first end face and the
second end face includes a first reflection coating film having a
reflectance of a degree that the stimulated emission light is
amplified, and laser light is output from each of the first end
face and the second end face.
11. The optical device according to claim 3, wherein the optical
element includes a ridge having a flare structure, and a width of
the ridge on the first end face side is set to be smaller than the
width of the ridge on the second end face side.
12. The optical device according to claim 1, wherein the optical
element is configured as a semiconductor laser.
13. The optical device according to claim 11, further comprising a
third lens in a region facing the light transmitting window on the
second end face side in the two light transmitting windows, and a
reflecting mirror in this order from the light transmitting window
side, wherein the second end face includes the antireflection film
on the surface, and the first end face includes a second reflection
coating film having a reflectance of a degree that an external
resonator is composed of the first end face and the reflecting
mirror in the light having the wavelength from 300 nm to 600 nm
both inclusive.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical device which
incorporates an optical element (for example, a semiconductor laser
or an optical amplifying element).
[0003] 2. Description of the Related Art
[0004] From the past, in the field of a semiconductor laser, a
solid laser represented by a titanium-sapphire laser has been
mainly used in a short wavelength. However, since the solid laser
is expensive and large, the semiconductor laser which is
inexpensive and small has been expected to come into practical use
in substitution for the solid laser. If the semiconductor laser
having the short wavelength is put into practical use, the
semiconductor laser may be used as a light source of a volume type
optical disk which corresponds to a next-generation high density
optical disk (blu-ray disk). Further, by using the semiconductor
laser together with a semiconductor laser having another wavelength
band, a convenient light source covering the entire wavelength band
of a visible light range may be realized, and it may be possible to
provide various light sources demanded in the field of medical
care, bioimaging, and the like.
[0005] However, in the semiconductor laser having the short
wavelength, it is not easy to obtain a high output as in the solid
laser. Thus, to obtain the high output, for example, it is
considered to use an optical amplifying element, and use an
external resonator (for example, refer to Japanese Unexamined
Patent Publication No. 2001-015833).
SUMMARY OF THE INVENTION
[0006] However, when the output of the semiconductor laser having
the short wavelength is increased, there is an issue that a drive
current and an optical output are varied with the passage of
time.
[0007] In view of the foregoing, it is desirable to provide an
optical device capable of suppressing a drive current and an
optical output from being varied with a passage of time.
[0008] According to an embodiment of the present invention, there
is provided an optical device including: an optical element; and a
pedestal including a supporting substrate supporting the optical
element, and a connecting terminal electrically connected to the
optical element. The optical element includes a first end face and
a second end face, and emits light having a wavelength of 430 nm or
less at least from the second end face in the first end face and
the second end face. Further, the optical device includes a sealing
section including a light transmitting window in each of a portion
facing the first end face and a portion facing the second end face,
and sealing the optical element.
[0009] In the optical device according to the embodiment of the
present invention, the optical element is sealed by the sealing
section, and the light transmitting window is provided in each of
the portion facing the first end face and the portion facing the
second end face in the sealing section. Therefore, it may be
possible to seal the optical element without inhibiting light
irradiation to the optical element, and light emission from the
optical element.
[0010] Here, in the optical device according to the embodiment of
the present invention, the optical element may serve an optical
amplifying element amplifying the light incident into the first end
face, and emitting the light having a luminance larger than that of
the incident light at least from the second end face in the first
end face and the second end face. Further, the optical element may
be configured as a semiconductor laser. However, in the case where
the optical element is configured as the semiconductor laser, a
third lens in a region facing the light transmitting window on the
second end face side in the two light transmitting windows, and a
reflecting mirror are preferably provided in this order from the
light transmitting window side. Further, the second end face
includes an antireflection film on the surface, and the first end
face preferably includes a second reflection coating film having a
reflectance of a degree that an external resonator is configured by
the first end face and the reflecting mirror in the light having
the wavelength of 430 nm or less.
[0011] According to the optical device of the embodiment of the
present invention, it may be possible to seal the optical element
without inhibiting the light irradiation to the optical element and
the light emission from the optical element. Therefore, it may be
possible to suppress a slight amount of a Si organic gas contained
in an external atmosphere from being reacted with the laser light
to generate a deposited material on the first end face and the
second end face. As a result, it may be possible to suppress a
drive current and an optical output from being varied with a
passage of time.
[0012] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional view of an optical amplifying
device in the longitudinal direction, according to a first
embodiment of the present invention.
[0014] FIG. 2 is a cross-sectional view of the optical amplifying
device of FIG. 1 in the transverse direction.
[0015] FIGS. 3A and 3B are cross-sectional views illustrating an
example of an optical amplifying element of FIG. 1.
[0016] FIG. 4 is a cross-sectional view illustrating another
example of the optical amplifying element of FIG. 1.
[0017] FIG. 5 is a cross-sectional view illustrating still another
example of the optical amplifying element of FIG. 1.
[0018] FIG. 6 is a schematic view illustrating the state in which
the optical amplifying device of FIG. 1 is installed on an optical
path of a light emitting device.
[0019] FIG. 7 is a characteristic view illustrating variation of
luminance deterioration caused by the passage of time in the case
where the optical amplifying element is sealed, and in the case
where the optical amplifying element is not sealed.
[0020] FIG. 8 is cross-sectional view illustrating a modification
of the optical amplifying device of FIG. 1.
[0021] FIG. 9 is a cross-sectional view illustrating another
modification of the optical amplifying device of FIG. 1.
[0022] FIG. 10 is a cross-sectional view of the light emitting
device in the longitudinal direction, according to a second
embodiment of the present invention.
[0023] FIG. 11 is a schematic view illustrating the state where an
external resonator is set in the light emitting device of FIG.
10.
[0024] FIGS. 12A and 12B are optical output spectrum views of the
optical amplifying device according to an example.
[0025] FIG. 13 is a relationship view between an output power and
an input power of the optical amplifying device according to the
example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Hereinafter, embodiments of the present invention will be
described in detail with reference to the drawings. The description
will be made in the following order.
1. First embodiment (optical amplifying device, FIGS. 1 to 2, 3A,
3B, 4 to 9) 2. Second embodiment (light emitting device, FIGS. 10
and 11) 3. Example (optical amplifying device, FIGS. 12A, 12B, and
13)
1. First Embodiment
Structure of an Optical Amplifying Device 1
[0027] FIG. 1 illustrates an example of the cross-sectional
structure of an optical amplifying device 1 in the longitudinal
direction, according to a first embodiment of the present
invention. FIG. 2 illustrates an example of the cross-sectional
structure of the optical amplifying device 1 of FIG. 1 in the
transverse direction. In addition, FIGS. 1 and 2 are schematic
illustrations, and the dimensions and the shapes are different from
actual dimensions and actual shapes.
[0028] The optical amplifying device 1 of this embodiment includes,
for example, a stem 10, an optical amplifying element 20, and a cap
30. The stem 10 corresponds to a specific example of "pedestal" of
the present invention. The optical amplifying element 20
corresponds to a specific example of "optical element" of the
present invention. The cap 30 corresponds to a specific example of
"sealing section" of the present invention.
[0029] The stem 10 constitutes a package of the optical amplifying
device 1 in corporation with the cap 30, and includes, for example,
a supporting substrate 11 supporting the optical amplifying element
20, and a plurality of connecting terminals 12. The supporting
substrate 11 has, for example, a square shape as illustrated in
FIG. 2, and a top face 11A of the supporting substrate 11 has such
a size that the cap 30 may be placed (fixed) on the top face 11A.
The plurality of connecting terminals 12 penetrate the supporting
substrate 11, for example, are projected long on the opposite side
from the top face 11A, and are projected short on the top face 11A
side. In the plurality of connecting terminals 12, a portion
projected long on the opposite side from the top face 11A
corresponds to a portion fitted into a substrate for a light source
or the like. Meanwhile, in the plurality of connecting terminals
12, a portion projected short on the top face 11A side corresponds
to a portion electrically connected to the optical amplifying
element 20 through wiring (not illustrated in the figure) or the
like. The plurality of connecting terminals 12 are supported by an
insulating member (not illustrated in the figure) provided in the
supporting substrate 11. The plurality of connecting terminals 12
and the supporting substrate 11 are insulated and separated from
each other by the above-described insulating member. Further, the
individual connecting terminals 12 are also insulated and separated
from each other by the above-described insulating member.
[0030] The optical amplifying element 20 is mounted on the top face
11A of the supporting substrate 11. For example, in the state of
being arranged on a sub-mount 21, the optical amplifying element 20
is mounted on the top face 11A. Although not illustrated in the
figure, the optical amplifying element 20 may be in direct contact
with the supporting substrate 11. The optical amplifying element 20
is generally referred to as a transmissive SOA (semiconductor
optical amplifier). This optical amplifying element 20 includes an
incidence-side end face 20A (first end face) and an emission-side
end face 20B (second end face), and emits light from the
emission-side end face 20B in the incidence-side end face 20A and
the emission-side end face 20B. The center wavelength (wavelength
.lamda.1) of the light (stimulated emission light) emitted from the
optical amplifying element 20 is, for example, from 300 nm to 600
nm both inclusive, preferably from 360 nm to 550 nm both inclusive,
and more preferably from 360 nm to 430 nm both inclusive. Further,
the optical amplifying element 20 amplifies the light incident into
the incidence-side end face 20A, and emits the light having a
luminance larger than that of the incident light from the
emission-side end face 20B.
[0031] As illustrated in FIGS. 3A and 3B, for example, the optical
amplifying element 20 includes semiconductor layers which include a
buffer layer 121, a lower cladding layer 122, a lower guiding layer
123, an active layer 124, an upper guiding layer 125, an upper
cladding layer 126, and a contact layer 127 on a substrate 120 in
this order from the substrate 120 side. Further, the optical
amplifying element 20 includes, for example, an electron barrier
layer 128 in the upper cladding layer 126. In addition, in the
optical amplifying element 20, layers other than the
above-described layers may be further provided, and a part of the
above-described layers (for example, the buffer layer 21, the
electron barrier layer 128, or the like) may be omitted.
[0032] The substrate 120 is made of, for example, a group III-V
nitride semiconductor having the wurtzite crystal structure, such
as GaN. Here, "group III-V nitride semiconductor" denotes a
semiconductor containing at least one kind selected from group 3B
elements in the short form periodic table, and at least N selected
from group 5B elements in the short form periodic table. Examples
of the group III-V nitride semiconductor include a gallium nitride
compound containing Ga and N. Examples of the gallium nitride
compound include GaN, AlGaN, AlGaInN. The group III-V nitride
semiconductor is doped with an n-type impurity such as Si, O, C,
Ge, Zn, and Cd, or a p-type impurity such as Mg, and Zn, if
necessary.
[0033] Like the substrate 120, the semiconductor layers on the
substrate 120 contain, for example, the group III-V nitride
semiconductor (for example, AlGaInN). The buffer layer 121 is
composed of, for example, an n-type GaN. The lower cladding layer
122 is composed of, for example, an n-type AlGaN. The lower guiding
layer 123 is composed of, for example, non-doped GaInN. The active
layer 124 is composed of, for example, a multiquantum well obtained
by alternately stacking a well layer and a barrier layer which are
formed of GaInN having composition ratios different from each
other, respectively. The barrier layer of the active layer 124 is,
for example, doped with the n-type impurity of approximately
1.times.10.sup.16 cm.sup.-3 to 5.times.10.sup.19 cm.sup.-3. In this
case, by the barrier layer of the active layer 124, it may be
possible to suppress the Quantum Stark effect by piezoelectricity,
which is applied to the quantum well.
[0034] The upper guiding layer 125 is composed of, for example,
non-doped GaInN. In the upper cladding layer 126, the layer on the
active layer 124 side is composed of, for example, the non-doped
GaInN in relation to the electron barrier layer 128. Meanwhile, in
the upper guiding layer 125, the layer on the contact layer 127
side is composed of, for example, an Mg doped GaN/AlGaN
superlattice in relation to the electron barrier layer 128. The
contact layer 127 is composed of, for example, Mg doped GaN. The
electron barrier layer 128 is composed of, for example, Mg doped
AlGaN.
[0035] Here, the lower guiding layer 123 and the upper guiding
layer 125 may have a thickness larger than a thickness generally
applied in a low-output type semiconductor layer for communication,
or the like. In this case, since the light confinement in the
stacking direction (vertical direction) is slightly weak, a beam
radiation half-value angle .theta..perp. in the vertical direction
is large (for example, 25 degrees or less). Depending on the degree
of the light confinement in the vertical direction, there is a case
where the transverse mode in the vertical direction becomes a
secondary or higher order mode. However, even in that case, in this
embodiment, the light is sufficiently confined at least by a ridge
129 in the transverse mode in the transverse direction, and the
transverse mode is a single mode.
[0036] In the upper part of the semiconductor layers on the
substrate 120, specifically, in the upper part of the upper
cladding layer 126 and the contact layer 127, the strip-shaped
ridge 129 is formed. The ridge 129 constitutes an optical waveguide
in corporation with portions located on both ends of the ridge 129
in the semiconductor layers on the substrate 120, performs the
light confinement in the transverse direction by utilizing the
refractive index difference in the transverse direction (direction
orthogonal to the resonator direction), and constricts a current
injected into the semiconductor layers on the substrate 120. In the
active layer 124, a portion immediately below the above-described
optical waveguide corresponds to a current injecting region, and
this current injecting region serves as a light emitting region
124A.
[0037] On the surfaces of both side faces of the ridge 129, and on
the surface of the vicinity of the ridge 129, an insulating film
130 is formed. The insulating film 130 is made of an insulating
material such as an oxide and a nitride, and is configured, for
example, by stacking SiO.sub.2 and Si in this order from the upper
cladding layer 126 side. The insulating film 130 basically protects
the optical amplifying element 20, but a function to suppress the
high order mode is given to the insulating film 130, if necessary.
Here, in the case where a material of the insulating film 130 is
selected so that an effective refractive index difference .DELTA.n
in the transverse direction is, for example, from 5.times.10.sup.-3
to 1.times.10.sup.-2 both inclusive, it can be said that the
insulating film 130 has the function to suppress the high order
mode.
[0038] When viewing the ridge 129 from the stacking direction of
the semiconductor layers, the ridge 129 is in a linear shape. The
ridge 129 extends, for example, in the direction parallel to an "m"
axis or a "c" axis (not illustrated in the figure) of the wurtzite
crystal structure. In addition, the ridge 129 may, for example,
extend in the direction intersecting the "m" axis or the "c" axis
of the wurtzite crystal structure at an angle within a range of
more than 0 degree and equal to or less than 45 degrees. In that
case, the ridge 129 preferably extends in the direction
intersecting the "m" axis or the "c" axis of the wurtzite crystal
structure at an angle within a range of more than 0 degree and
equal to or less than 10 degrees.
[0039] The length (device length) of the ridge 129 is, for example,
within a range from 300 .mu.m to 10 nm both inclusive, and is, for
example, 3 mm. For example, as illustrated in FIG. 3A, the width of
the ridge 129 is narrow in the vicinity of the incidence-side end
face 20A, and becomes wide from the incidence-side end face 20A
toward the emission-side end face 20B. In other words, in this
case, the ridge 129 has a so-called flare structure. In addition,
the ridge 129 may not extend in the direction orthogonal to the
incidence-side end face 20A and the emission-side end face 20B, for
example, as illustrated in FIG. 3A, and the ridge 129 may extend in
the direction obliquely intersecting the incidence-side end face
20A and the emission-side end face 20B, for example, as illustrated
in FIG. 4. For example, as illustrated in FIG. 5, the width of the
ridge 129 may be narrow in the middle section in the longitudinal
direction (resonator direction), and may be wide in the vicinity of
the end faces of both the incidence-side end face 20A and the
emission-side end face 20B, in comparison with the middle
section.
[0040] A width W1 of the ridge 129 on the incidence-side end face
20A side is smaller than a width W2 of the ridge 129 on the
emission-side end face 20B side. For example, the width W1 is 2
.mu.m or less. For example, when the device length is 3 mm, the
width W1 is approximately 1.4 .mu.m. For example, the width W2 is
1000 .mu.m or less, and preferably 10 .mu.m or less. For example,
when the device length is 3 mm, the width W2 is approximately 5
.mu.m.
[0041] In the semiconductor layers on the substrate 120, the pair
of the incidence-side end face 20A and the emission-side end face
20B sandwiching the ridge 129 from the extending direction of the
ridge 129 are formed. The incidence-side end face 20A and the
emission-side end face 20B are formed by cutting a wafer (not
illustrated in the figure) in a manufacturing process, and are, for
example, cleaved faces formed by cleavage. The resonator is
composed of the incidence-side end face 20A and the emission-side
end face 20B in the stacked plane direction.
[0042] The incidence-side end face 20A is a face into which the
light output from a light emitting device 2 which will be described
later is incident, and an antireflection film 133 is formed on the
surface of the incidence-side end face 20A. Meanwhile, the
emission-side end face 20B is a face from which the laser light is
emitted, and an antireflection film 134 is formed on the surface of
the emission-side end face 20B. The antireflection films 133 and
134 are configured by stacking one or a plurality of films made of
the oxide or the nitride. The antireflection films 133 and 134
have, for example, a one-layer structure of Al.sub.2O.sub.3,
SiO.sub.2, MN, or the like. Alternatively, the antireflection films
133 and 134 have, for example, a two-layer structure of
TiO.sub.2/Al.sub.2O.sub.3, ZrO.sub.2/SiO.sub.2,
Ta.sub.2O.sub.3/SiO.sub.2, or the like. Therefore, when the light
output from the light emitting device 2 which will be described
later, and the light output from the optical amplifying element 20
are vertically incident into the antireflection films 133 and 134,
the antireflection films 133 and 134 transmit the light at a
reflectance of, for example, 10.sup.-3 (0.1%) or less.
[0043] On the top face (surface of the contact layer 127) of the
ridge 129, an upper electrode 131 is provided. The upper electrode
131 is, for example, configured by stacking Ti, Pt, and Au in this
order, and is electrically connected to the contact layer 127.
Meanwhile, on the rear surface of the substrate 120, a lower
electrode 132 is provided. The lower electrode 132 is, for example,
configured by stacking an alloy of Au and Ge, Ni, and Au in this
order from the substrate 120 side, and is electrically connected to
the substrate 120.
[0044] The surface of the contact layer 127 as being the top face
of the optical amplifying element 20, and the rear surface of the
substrate 120 as being the bottom face of the optical amplifying
element 20 are, for example, "c" planes of the wurtzite crystal
structure, and the incidence-side end face 20A and the
emission-side end face 20B are "m" planes of the wurtzite crystal
structure at this time. Further, the top face and the bottom face
of the optical amplifying element 20 are, for example, the "m"
planes or the "c" planes of the wurtzite crystal structure, and the
incidence-side end face 20A and the emission-side end face 20B are
the "c" planes of the wurtzite crystal structure at this time.
[0045] Here, in the case where the incidence-side end face 20A and
the emission-side end face 20B are the "m" planes of the wurtzite
crystal structure, when the ridge 129 extends in the direction
intersecting the "m" axis of the wurtzite crystal structure, the
ridge 129 extends in the direction obliquely intersecting the
incidence-side end face 20A and the emission-side end face 20B, for
example, as illustrated in FIG. 4. In the same manner, in the case
where the incidence-side end face 20A and the emission-side end
face 20B are the "c" planes of the wurtzite crystal structure, when
the ridge 129 extends in the direction intersecting the "c" axis of
the wurtzite crystal structure, the ridge 129 extends in the
direction obliquely intersecting the incidence-side end face 20A
and the emission-side end face 20B, for example, as illustrated in
FIG. 4.
[0046] The optical amplifying element 20 is arranged in such a
manner that an optical axis AX1 parallel to a normal of the
incidence-side end face 20A and the emission-side end face 20B
becomes parallel to the top face 11A, and the optical amplifying
element 20 outputs the light in the direction parallel to the top
face 11A. As illustrated in FIG. 2, the optical amplifying element
20 is preferably arranged in such a manner that the optical axis
AX1 intersects a normal AX2 of a light transmitting window 32 which
will be described later at an angle .theta.
(0.degree.<.theta..ltoreq.45.degree.). In other words, the
optical amplifying element 20 is preferably arranged in such a
manner that the incidence-side end face 20A is directed in the
direction that the incidence-side end face 20A and the light
transmitting window 32 do not frontally face each other. This is
because a phenomenon that the light incident into the
incidence-side end face 20A returns to the light source which is
not illustrated in the figure, that is, generation of so-called
returning light may be eliminated. However, in the case where
generation of the returning light is not an issue, although not
illustrated in the figure, the optical amplifying element 20 may be
arranged in such a manner that the optical axis AX1 is parallel to
the normal AX2.
[0047] The cap 30 seals the optical amplifying element 20. The cap
30 includes a tube 31 in which an aperture 31A is provided in each
of a portion facing the incidence-side end face 20A, and a portion
facing the emission side end face 20B. The lower end of the tube 31
is fixed onto the top face 11A, and the optical amplifying element
20 is positioned in an internal space 31B of the tube 31. The
internal space 31B is filled with, for example, a Si organic
compound gas having an extremely-low vapor pressure.
[0048] The cap 30 includes the light transmitting windows 32
arranged so as to close the two apertures 31A provided on the side
faces of the tube 31. For example, as illustrated in FIGS. 1 and 2,
the light transmitting windows 32 are arranged in the internal
space 31B of the tube 31, and have a function to transmit the light
incident into the incidence-side end face 20A of the optical
amplifying element 20, and the light output from the emission-side
end face 20B of the optical amplifying element 20. For example,
although not illustrated, on the surface, the light transmitting
windows 32 contain a transparent member in which antireflection
films having the same function as the antireflection films 133 and
134 which are formed in the optical amplifying element 20 are
formed.
[0049] For example, as illustrated in FIG. 6, the optical
amplifying device 1 of this embodiment is arranged on the optical
axis of light L having a short wavelength (430 nm or less) output
from the light emitting device 2. Specifically, the two light
transmitting windows 32 provided in the cap 30 are arranged on the
optical axis of the light emitting device 2, and the light
transmitting window 32 on the incidence-side end face 20A side of
the optical amplifying element 20 in the two light transmitting
windows 32 is directed toward the light emitting device 2 side.
Further, the optical amplifying device 1 is arranged in such a
manner that the normal AX2 (not illustrated in FIG. 6) of the light
transmitting window 32 on the incidence-side end face 20A side is
parallel to the optical axis of the light L output from the light
emitting device 2.
[0050] On the optical axis of the light emitting device 2, for
example, three lenses 3, 4, and 5 are arranged. The lens 3
parallelizes the laser light L output from the light emitting
device 2. The lens 4 condenses the light parallelized by the lens
3, and guides the light to the incidence-side end face 20A. The
lens 5 parallelizes the light amplified by the optical amplifying
device 1, and output from the emission-side end face 20B. In
addition, the lens 5 may be omitted depending on the intended
use.
[0051] The lenses 4 and 5 are, for example, arranged in such a
manner that the optical axis of the lenses 4 and 5 is directed in
the direction intersecting the normal (optical axis AX1) of the
emission-side end face 20B at the angle .theta. defined by the
following equation.
sin .theta.=sin .alpha..times.(n.sub.1/n.sub.2)
[0052] Here, .alpha. is an angle between the normal (optical axis
AX1) of the emission-side end face 20B and a line parallel to the
extending direction of the ridge 129. n.sub.1 is the refractive
index of a material constituting the optical path of the optical
amplifying element 20. n.sub.2 is the refractive index of a gas in
contact with the surface of the lens 5 on the optical amplifying
element 20 side.
[0053] (Structure of the Light Emitting Device 2)
[0054] For example, as illustrated in FIG. 6, the light emitting
device 2 includes, for example, a stem 40, a light emitting element
50, and a cap 60.
[0055] The stem 40 constitutes the package of the light emitting
device 2 in corporation with the cap 60, and includes, for example,
a supporting substrate 41 supporting the light emitting element 50,
and a plurality of connecting terminals 42. The plurality of
connecting terminals 42 are electrically connected to the light
emitting element 50 through the wiring (not illustrated in the
figure) or the like. The light emitting element 50 converts the
electrical signal into the optical signal to output the optical
signal, and outputs, for example, the light in the direction
parallel to the normal of the supporting substrate 41. The light
emitting element 50 is, for example, an edge emitting semiconductor
laser, and arranged in such a manner that the optical axis is
parallel to the normal of the supporting substrate 41. Although not
illustrated in the figure, the light emitting element 50 includes
the front end face and the rear end face, and emits light from the
front end face.
[0056] A wavelength .lamda.2 of the light emitted from the light
emitting element 50 is, for example, from 300 nm to 600 nm both
inclusive, preferably from 360 nm to 550 nm both inclusive, and
more preferably from 360 nm to 430 nm both inclusive. The
wavelength .lamda.2 has a value within a range of .lamda.1.+-.5 nm,
and preferably has a value within a range of .lamda.1.+-.2 nm.
Further, the wavelength .lamda.2 is preferably longer than the
wavelength .lamda.1.
[0057] Like the optical amplifying element 20, the light emitting
element 50 contains AlGaInN. Although not illustrated in the
figure, for example, in the light emitting element 50, the stacked
body including the AlGaInN active layer is formed on the GaN
substrate. Although not illustrated in the figure, for example,
each of the front end face and the rear end face is provided with
the reflection coating film arranged on its surface. Here, when the
current is injected into the light emitting element 50, and the
light emission is generated in the active layer, the reflection
coating film has a reflectance of such a degree that the light
emitting element 50 is laser-oscillated by the emitted light
repeatedly reflecting on the front end face and the rear end face.
In this manner, by providing the reflection coating films on the
front end face and the rear end face, the light emitting element 50
may perform the gain switching operation or the self pulsation
operation. Although not illustrated in the figure, for example, the
reflection coating film may be provided on the surface of the rear
end face, and although not illustrated in the figure, for example,
a film (non-reflection coating film) having the same function as
the antireflection films 133 and 134 may be provided on the surface
of the front end face. In this case, the external resonator is set
by inserting a translucent mirror between the lens 3 and the lens
4, and therefore the light emitting element 50 may perform the
mode-locked operation.
[0058] The cap 60 seals the light emitting element 50. The cap 60
includes, for example, a tube 61 in which an aperture is provided
in each of the upper end and the lower end. The lower end of the
tube 61 is fixed onto the top face of the supporting substrate 41,
and the light emitting element 50 is positioned in the internal
space of the tube 61. The cap 60 includes a light transmitting
window 62 arranged so as to close the aperture 61A on the upper end
side of the tube 61. As illustrated in FIG. 6, for example, the
light transmitting window 62 is arranged in the light emission
direction of the light emitting element 50, and has a function to
transmit the light output from the light emitting element 50.
[0059] The optical amplifying device 1 of this embodiment may be
manufactured, for example, as will be described next. First, after
preparing the stem 10, the optical amplifying element 20, and the
cap 30, the optical amplifying element 20 is mounted on the top
face of the supporting substrate 11, and then the optical
amplifying element 20 is sealed by the cap 30. Next, in dry air,
the lower end (lower end of the tube 31) of the cap 30 and the top
face 11A of the supporting substrate 11 are bonded to each other by
electrical welding. In this manner, the optical amplifying device 1
of this embodiment is manufactured.
[0060] (Operation of the Optical Amplifying Device 1)
[0061] Next, with reference to FIG. 6, the operation of the optical
amplifying device 1 will be described. First, when the electrical
signal is input from the external to the light emitting element 50
in the light emitting device 2, the electrical signal is converted
into the optical signal in the light emitting element 50, and the
laser light L having the wavelength .lamda.2 is output from the
light emitting element 50 to the external through the light
transmitting window 62. The laser light L output to the external is
parallelized by the lens 3, condensed by the lens 4, and incident
into the light transmitting window 32 of the optical amplifying
device 1. After the light incident into the light transmitting
window 32 transmits the light transmitting window 32, the light is
incident into the incidence-side end face 20A of the optical
amplifying element 20, is amplified by the optical amplifying
element 20, and is output as the laser light having the wavelength
.lamda.1 to the external through the light transmitting window 32.
The light output to the external is parallelized by the lens 5, and
then incident into another device (not illustrated in the figure).
In this manner, the laser light L output from the light emitting
device 2 is amplified by the optical amplifying device 1.
[0062] Here, the optical amplifying element 20 is driven with a DC
signal or a pulse signal. For example, a high-frequency signal
having a pulse width of 20 ns, and a repetition frequency of 1 MHz
is input as the pulse signal to the optical amplifying element 20.
In the light emitting element 50, an optical pulse is output by the
mode-locked operation, the gain switching operation, or the self
pulsation operation, if necessary. This optical pulse is incident
into the optical amplifying element 20, and thus the optical pulse
having a high peak power is output from the optical amplifying
element 20.
[0063] (Effects of the Optical Amplifying Device 1)
[0064] Next, the effects of the optical amplifying device 1 will be
described. In this embodiment, the optical amplifying element 20 is
sealed by the stem 10 and the cap 30, and the light transmitting
window 32 is provided in each of the portion facing the
incidence-side end face 20A and the portion facing the
emission-side end face 20B in the cap 30. Therefore, it may be
possible to seal the optical amplifying element 20 without
inhibiting the light irradiation to the optical amplifying element
20, and the light emission from the optical amplifying element 20.
As a result, a slight amount of a Si organic gas contained in an
external atmosphere is suppressed from being reacted with the laser
light to generate a deposited material on the incidence-side end
face 20A and the emission-side end face 20B.
[0065] In particular, generation of the deposited material becomes
an issue on the end faces like the incidence-side end face 20A and
the emission-side end face 20B, where the antireflection films 133
and 134 are formed, and the reflectance is low. For example, in the
case where the optical amplifying element 20 is exposed to the
external atmosphere without providing the cap 30, the slight amount
of the Si organic gas contained in the external atmosphere is
reacted with the laser light. Therefore, the deposited material is
generated on the incidence-side end face 20A and the emission-side
end face 20B, and the reflectance on the incidence-side end face
20A and the emission-side end face 20B is changed due to the
deposited material. Due to the change of the reflectance on the
incidence-side end face 20A and the emission-side end face 20B, the
drive current of the optical amplifying element 20 is changed, and
the optical output is changed (reduced), for example, as
illustrated with a broken line of FIG. 7.
[0066] Meanwhile, in this embodiment, the optical amplifying
element 20 is sealed by the stem 10 and the cap 30, and generation
of the deposited material on the incidence-side end face 20A and
the emission-side end face 20B is suppressed. Therefore, it may be
possible to suppress the change of the drive current of the optical
amplifying element 20, and, further, it may be possible to suppress
the change (reduction) of the optical output, as illustrated with
the solid line of FIG. 7.
[0067] In this embodiment, in the case where the ridge 129 of the
optical amplifying element 20 has the flare structure, and the
width on the incidence-side end face 20A side is smaller than the
width on the emission-side end face 20B side in the flare
structure, it may be possible to output the laser light having the
high output while maintaining the single-transverse mode at least
in the width direction. Further, since the single-transverse mode
is maintained at least in the width direction, it may be possible
to realize high optical coupling efficiency between the optical
amplifying element 20 and another optical system.
[0068] (Modification of the First Embodiment)
[0069] In the foregoing embodiment, although only the optical
amplifying element 20 and the sub-mount 21 are provided in the
internal space 31B of the tube 31, for example, as illustrated in
FIG. 8, the lenses 4 and 5 may be provided. At this time, the lens
4 is provided between the incidence-side end face 20A and the light
transmitting window 32, and the lens 5 is provided between the
emission-side end face 20B and the light transmitting window 32. To
align the optical axis AX1 of the optical amplifying element 20 and
the optical axis of the lenses 4 and 5, a sub-mount 22 may be
additionally provided between the optical amplifying element 20 and
the sub-mount 21. For example, as illustrated in FIG. 9, in
substitution for the lenses 4 and 5, lenses 33 and 34 having shapes
which may be fitted into the apertures 31A of the tube 31 may be
set in the apertures 31A. In this case, when the light transmitting
windows 32 and the lenses 33 and 34 are conceptually combined, it
can be said that a combination of the light transmitting window 32
and the lens 33 or 34 is a light transmitting window having a lens
function. At this time, the lenses 33 and 34 may be bonded onto the
light transmitting windows 32 with an adhesive (not illustrated in
the figure). Therefore, it may be possible to reduce the number of
steps necessary for positioning the lenses 4 and 5, in comparison
with the case where the lenses 4 and 5 are provided separately from
the optical amplifying device 1 as in the foregoing embodiment.
[0070] In the foregoing embodiment, although the optical amplifying
element 20 is a so-called transmissive SOA, for example, the
optical amplifying element 20 may be a so-called resonant SOA,
although not illustrated in the figure. However, in this case,
although not illustrated in the figure, the incidence-side end face
20A and the emission-side end face 20B include reflection coating
films (first reflection coating films) on the surface, in
substitution for the antireflection films 133 and 134. Here, when
the light having a predetermined wavelength (from 300 nm to 600 nm
both inclusive) is incident into the incidence-side end face 20A,
and stimulated emission is generated in the active layer by the
incident light, the reflection coating film has a reflectance of
such a degree that the stimulated emission light is amplified by
repeatedly reflecting on the incidence-side end face 20A and the
emission-side end face 20B, and the laser light is output from both
the incidence-side end face 20A and the emission-side end face
20B.
2. Second Embodiment
Structure of a Light Emitting Device 6
[0071] FIG. 10 illustrates an example of the cross-sectional
structure of a light emitting device 6 in the longitudinal
direction, according to a second embodiment of the present
invention. In addition, FIG. 10 is a schematic illustration, and
the dimensions and the shapes are different from actual dimensions
and actual shapes.
[0072] The structure of the light emitting device 6 of this
embodiment is different from that of the optical amplifying device
1 of the foregoing embodiment in that a light emitting element 70
is provided in substitution for the optical amplifying element 20
of the light emitting device 1 of the foregoing embodiment. Thus,
hereinafter, the difference from the foregoing embodiment will be
mainly described, and description of the points common to those of
the foregoing embodiment will be appropriately omitted.
[0073] The light emitting element 70 converts the electrical signal
into the optical signal to output the optical signal, and outputs,
for example, the light in the direction parallel to the top face
11A of the supporting substrate 11. The light emitting element 70
is, for example, the edge emitting semiconductor laser, and is
arranged in such a manner that the optical axis is parallel to the
top face 11A. The light emitting element 70 includes an
emission-side end face 70A and a transmission-side end face 70B,
and emits the light from the incidence-side end face. The center
wavelength of the light (stimulated emission light) emitted from
the light emitting element 70 is, for example, from 300 nm to 600
nm both inclusive, preferably from 360 nm to 550 nm both inclusive,
and more preferably from 360 nm to 430 nm both inclusive. Like the
optical amplifying element 20, the light emitting element 70
contains AlGaInN, and, in the light emitting element 70, for
example, the stacked body including the AlGaInN active layer is
formed on the GaN substrate, although not illustrated in the
figure. Although not illustrated in the figure, for example, the
transmission-side end face 70B includes the antireflection film
(second reflection coating film) having the same function as the
antireflection films 133 and 134 on the surface. Meanwhile,
although not illustrated in the figure, the emission-side end face
70A includes the reflection coating film on the surface. Here, when
the current is injected into the light emitting element 70, and the
light emission is generated in the active layer, the reflection
coating film has the reflectance of such a degree that the light
emitting element 70 is laser-oscillated by the emitted light
repeatedly reflecting on the emission-side end face 70A and a
reflecting mirror 7 which will be described later, and the laser
light is output from the emission-side end face 70A. In other
words, here, the reflection coating film has the reflectance of
such a degree that the external resonator is composed of the
emission-side end face 70A and the reflecting mirror 7 which will
be described later in the light having the predetermined
wavelength. Here, for example, the predetermined wavelength is from
300 nm to 600 nm both inclusive, preferably from 360 nm to 550 nm
both inclusive, and more preferably from 360 nm to 430 nm both
inclusive.
[0074] For example, as illustrated in FIG. 11, the light emitting
device 6 of this embodiment is used together with the reflecting
mirror 7, and the lenses 8 and 9. The reflecting mirror 7 and the
lens 8 are arranged in the space outside the light emitting device
6, and on the transmission-side end face 70B side. The reflecting
mirror 7 and the lens 8 are arranged in the region facing the light
transmitting window 32 on the transmission-side end face 70B side
in the two light transmitting windows 32. The reflecting mirror 7
and the lens 8 are arranged on the optical axis (not illustrated in
the figure) of the light emitting element 70, and the lens 8 is
arranged closer on the light emitting device 6, in comparison with
the reflecting mirror 7. Meanwhile, the lens 9 is arranged in the
space outside the light emitting device 6, and on the emission-side
end face 70A side. The lens 9 is arranged in the region facing the
light transmitting window 32 on the emission-side end face 70A side
in the two light transmitting windows 32. The lens 9 is also
arranged on the optical axis (not illustrated in the figure) of the
light emitting element 70.
[0075] Here, for example, the lens 8 parallelizes the laser light
output from the transmission-side end face 70B of the light
emitting device 6. It is enough for the lens 8 to adjust the
emission angle of the incident light, and the lens 8 may not
parallelize the incident light in a strict sense. The reflecting
mirror 7 reflects the light parallelized by the lens 8 so that the
light returns to the lens 8, and constitutes the external resonator
in corporation with the emission-side end face 70A. The lens 9
parallelizes the laser light output from the emission-side end face
70A of the light emitting device 6. In addition, the lens 9 may be
omitted depending on the intended use.
[0076] (Operation of the Light Emitting Device 6)
[0077] Next, with reference to FIG. 11, the operation of the light
emitting device 6 will be described. First, when the electrical
signal is input from the external to the light emitting element 70
in the light emitting device 6, the electrical signal is converted
into the optical signal in the light emitting element 70, and the
laser light is output from the transmission-side end face 70B of
the light emitting element 70 to the external through the light
transmitting window 32. After the laser light output to the
external is parallelized by the lens 8, the laser light is
reflected by the reflecting mirror 7, and returns to the light
emitting element 70. The stimulated emission is generated in the
active layer by the light which returns to the light emitting
element 70. The light emitting element 70 is laser-oscillated by
the stimulated emission light repeatedly reflecting on the
emission-side end face 70A and the reflecting mirror 7, and the
laser light is output from the emission-side end face 70A. In this
manner, the laser oscillation is generated in the light emitting
device 6.
[0078] (Effects of the Light Emitting Device 6)
[0079] Next, the effects of the light emitting device 6 will be
described. In this embodiment, the light emitting element 70 is
sealed by the stem 10 and the cap 30, and the light transmitting
window 32 is provided in each of the portion facing the
emission-side end face 70A and the portion facing the
transmission-side end face 70B in the cap 30. Therefore, it may be
possible to seal the light emitting element 70 without inhibiting
the light incidence into the light emitting element 70, and the
light emission from the light emitting element 70. As a result, the
slight amount of the Si organic gas contained in the external
atmosphere is suppressed from being reacted with the laser light to
generate the deposited material on the emission-side end face 70A
and the transmission-side end face 70B.
3. Examples
[0080] Next, examples 1 and 2 of the optical amplifying device 1
according to the first embodiment will be described. In the
examples 1 and 2, in the optical amplifying device 1 according to
the first embodiment, the device length was 3 mm, and the ridge 129
had the flare structure. In the example 1, as illustrated in FIG.
3A, for example, the ridge 129 was a straight type. In the example
2, as illustrated in FIG. 4, for example, the ridge 129 was an
oblique waveguide type.
[0081] In both of the examples 1 and 2, CW light having the
wavelength of 404 nm is input to the incidence-side end face 20A,
and a spectrum of the light output at this time from the optical
amplifying device 1 of the examples 1 and 2 was measured. The
results of the example 1 at that time were indicated in FIG. 12A,
and the results of the example 2 were indicated in FIG. 12B.
Further, the magnitude of the drive current input to the optical
amplifying device 1 of the example 1 was varied, and the output
power at that time was measured. The results were indicated in FIG.
13.
[0082] From FIGS. 12A and 12B, it can be seen that the high-power
longitudinal mode structure determined by the device length is
notably displayed in the straight type optical amplifying device 1,
but the longitudinal mode structure is hardly seen in the optical
amplifying device 1 in which the waveguide is obliquely formed.
This indicates that the depth of the longitudinal mode is reduced
by obliquely forming the waveguide, and the residual reflection of
the end face is suppressed.
[0083] From FIG. 13, the tendency that the output was saturated was
seen when the input power was 300 mW or less, and the maximum
output was approximately 200 mW when the input power was 12 W, and
the drive current was 500 mA. Therefore, when it is desired to use
the characteristic that the output power is linearly increased to
the input power, the low current injecting region of the optical
amplifying device 1 may be utilized, and when it is desired to
stably utilize the higher output, the high current injecting region
may be utilized.
[0084] The present application contains subject matter related to
that disclosed in Japanese Priority Patent Application JP
2009-250624 filed in the Japan Patent Office on Oct. 30, 2009 and
Japanese Priority Patent Application JP 2010-045394 filed in the
Japan Patent Office on Mar. 2, 2010, the entire contents of which
is hereby incorporated by references.
[0085] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alternations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *